Unable to restore WhatsApp chat history from iCloud

Hi, my wife and I have just changed mobile (cellular) service providers for our iPhones and have now successfully ported over our previous phone numbers (with Community help!).

Following on from this switch, my wife has lost all her WhatsApp chat history.

Here is an account of how she reached this stage. I've been Googling but so far to no avail. Hopefully you can help with this.

PS. sorry about the point numbering, it's a Notes issue that won't go away :)

By the way, it's an iPhone XS on ios 15.4.1:

"Loss of WhatsApp chat history following switch to Virgin.

Having instigated my switch of cellular service provider from Vodafone to Virgin, I changed the phone number in WhatsApp settings to my new, temporary, Virgin number.

I then realised that the number change in WhatsApp had locked me out of certain WhatsApp groups that had number specific settings. I informed the group administrator who changed the group settings to the temporary number.

He said that when the old (ported) number was restored to simply change it back in WhatsApp (ie. step 1 (first) in reverse). I have never done this however, because I deleted the App (under advice from the Administrator, “to avoid unnecessary admin”).

He then advised me to reinstall WhatsApp, but making sure that the app was backed up to prevent losing all past conversations.

I checked my WhatsApp settings and saw that monthly back-ups were switched on. I also did a manual backup immediately prior to deleting the app.

I then deleted the app and re-installed it, but the option to restore backups was greyed out along with the message “No Backup Found”

It became apparent that what we had thought would be an immediate switch, back to my original phone number (porting), might take some days and figured this problem may be something to do with that delay.

I ordered a new sim to try and solve this problem.

This sim is now activated and all aspects of iPhone life are fine, with the exception of this issue; ie. the WhatsApp chat history Backup cannot be found in my iCloud backup.

Edit:

Ok, I’ve a feeling I’ve made this question appear over-complicated by giving so much information; here is the heart of it:

1. When trying to restore chat history, the app says “no backups found”

2. However the device has a record of WhatsApp backups totalling nearly 800Mb

Any ideas why the app can’t see the backups?